It is a conventional practice to apply a resin material sheet for protection of the surface of a member such as a metal plate, a coated metal plate, an aluminum sash, a resin board, a decorative copper plate, a vinyl chloride-laminated steel plate, a glass plate and the like during transportation, processing, covering and the like.
The property necessary for a surface protection sheet includes absence of detachment and delamination of a protection sheet after application to an application object and absence of a residual adhesive layer on the application object after release or removal. Furthermore, it includes absence of the development of detachment and delamination of a surface protection sheet, damage, and adhesive residue on an application object and the like, after processing of the application object with the surface protection sheet applied thereto. For example, JP-A-2000-328022 and JP-A-2002-302657 disclose a surface protection sheet for a metal plate.
Of the processing methods for a plate member and the like, laser cutting processing has superior merits. The merits are, unlike punching processing, it does not require various dies but merely requires an input of the design data for practicing, it requires a shorter time than punching processing when a processing target (hereinafter to be also referred to as a workpiece) is particularly a metal plate, it is applicable even when the workpiece is thick, and it does not require a lubricant. Accordingly, the market of the laser cutting processing tends to expand. However, laser cutting processing requires a high-pressure (about 0.5-1.5 MPa) assist gas supply.
In some cases, a workpiece is desirably subjected to laser cutting processing with a surface protection sheet applied thereon for appearance reasons and the like. In such a case, there is a problem of undesired delamination of the surface protection sheet from the workpiece due to the influence of the assist gas. To solve such problem, JP-A-2-295688, JP-A-7-241688 and JP-A-2001-212690 propose laser cutting processing methods capable of suppressing delamination during laser cutting processing. These processing methods can suppress delamination of a protection sheet.